The development of a new pharmaceutical agent requires careful optimization of the chemical and biological properties of a lead compound. For example, a successful drug candidate must be safe and effective for its intended use. Further, the compound must possess desired pharmacokinetic and pharmacodynamic profiles. This arduous development process usually requires extensive experimentation. In many cases, the process for determining the optimal compound can often require preparation of thousands of structurally similar compounds.
Among the properties that can limit the utility of a potential pharmaceutical agent is the degree to which the compound is complexed to proteins in vivo. If a high percentage of the compound present in vivo is non-specifically bound, for example by components of blood and blood plasma, this leaves only a very small amount of free compound available to tissue to perform its therapeutic function. Thus, binding of the compound to various proteins and other plasma components may require an unacceptably large dosage of compound to achieve the desired therapeutic effect.
Traditional Approaches have Sought to Alter Pharmacokinetic Properties.
The Rho-associated kinase is a key intracellular regulator of cytoskeletal dynamics and cell motility. Rho-kinase regulates a number of downstream targets of RhoA through phosphorylation, including, for example, myosin light chain, the myosin light chain phosphatase binding subunit and LIM-kinase 2. In smooth muscle cells Rho-kinase mediates calcium sensitization and smooth muscle contraction. Inhibition of Rho-kinase blocks 5-HT and phenylephrine agonist induced muscle contraction. When introduced into non-smooth muscle cells, Rho kinase induces stress fiber formation and is required for the cellular transformation mediated by RhoA. Rho kinase participates in a variety of cellular processes, including but not limited to Na/H exchange transport system activation, stress fiber formation, adducin activation. Rho kinase is involved in physiological processes such as vasoconstriction, bronchial smooth muscle constriction, vascular smooth muscle and endothelial cell proliferation, platelet aggregation, and others.
Inhibition of Rho-kinase activity in animal models has demonstrated a number of benefits of Rho-kinase inhibitors for the treatment of human diseases. These include models of cardiovascular diseases such as hypertension, atherosclerosis, restenosis, cardiac hypertrophy, ocular hypertension, cerebral ischemia, cerebral vasospasm, penile erectile dysfunction, central nervous system disorders such as neuronal degeneration and spinal cord injury, and in neoplasias where inhibition of Rho-kinase activity has been shown to inhibit tumor cell growth and metastasis, angiogenesis, arterial thrombotic disorders such as platelet aggregation and leukocyte aggregation, asthma, regulation of intraoccular pressure, and bone resorption. The inhibition of Rho-kinase activity in patients has benefits for controlling cerebral vasospasms and ischemia following subarachnoid hemorrhage.
In mammals, Rho-kinase consists of two isoforms, ROCK1 (ROCKβ; p160-ROCK) and ROCK2 (ROCKα). ROCK1 and ROCK2 are differentially expressed and regulated in specific tissues. For example, ROCK1 is ubiquitously expressed at relatively high levels, whereas ROCK2 is preferentially expressed in cardiac and brain tissues and in a developmental stage specific manner. ROCK1 is a substrate for cleavage by caspase-3 during apoptosis, whereas ROCK2 is not. Smooth muscle specific basic calponin is phosphorylated only by ROCK2.
Further, the physiological roles of the proteins appear to be distinct. For example, a recent study comparing the ROCK1/+ haploinsufficient mice with wild type littermates indicated that ROCK1 is critical for the development of cardiac fibrosis, but not hypertrophy, in response to various pathological conditions and suggest that signaling pathways leading to the hypertrophic and profibrotic response of the heart are distinct. However, the lack of inhibitors specific for ROCK1 or ROCK2 has impeded their respective roles to otherwise be distinguished.
Accordingly, there is a need for improved ROCK specific kinase inhibitors, including kinase inhibitors that specifically inhibit ROCK1 or ROCK2.